Mirai Choujuu Fobia / Phobia

The hentai is based on the manga or story of the same name by U-Jin, a manga artist and screenwriter popular in the 90s (Shin Angel, Angel, Visionary, Kojin Jugyou). 

Ijima is not just an ordinary student; she came from the future, where humanity is on the brink of extinction and the planet is taken over by terrifying monsters - replinoids. She arrived in the past to find the chosen one who can use the artifact - the sword of the great hero - to save the world and all humanity. Ijima finds him quickly - he turns out to be an ordinary but very perverted boy, Narita-kun.